JP2014230340A - Control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuation in an output current when switching from peak current control to PI control or switching from the PI control to the peak current control for controlling an insulation DC-DC converter including a switching element.SOLUTION: In a control method having first control combined with second control, a value of the first control is fit to a value of the second control when switching from the first control to the second control.

Description

  The present invention relates to a switching control method for two controls.

  There are various types of control of an insulation type DC-DC converter including a switching element. For example, in the peak current control, the duty ratio of the control signal of the switching element is adjusted by using the change in the output current from the output current of the current control cycle to the target output current (target current) of the next control cycle. Thus, the output current of the next control cycle is controlled, and the robustness can be improved.

  However, in the peak current control, if the discontinuous mode that fluctuates including the period when the target current becomes small and the output current becomes zero, the change in the output current cannot be obtained correctly and the responsiveness becomes low. Becomes difficult to follow the target current.

  In addition, there is PI control as control of an insulation type DC-DC converter including a switching element. In PI control, the output current is controlled by performing proportional control and integral control so that the difference between the output current and the target current becomes zero, and the output current is changed to the target current even in the discontinuous mode. Can be followed.

However, since PI control is low in robustness, the output current ripple may increase due to the influence of fluctuations in the load and input power.
Therefore, normally, peak current control with high robustness is performed, switching to PI control with high responsiveness when the target current becomes small, and switching from PI control to peak current control when the target current returns to the original size. It is possible to switch.

  However, in the peak current control, the output current follows the target current with a certain error, and in the PI control, the output current follows the target current so that the peak current control is switched to the PI control. When switching to control, the output current fluctuates.

  For example, Japanese Patent Application Laid-Open No. 2004-133867 discloses a technique related to control that includes a switching element and switches the current mode of the current flowing through the boost reactor to any one of a continuous mode, a critical mode, and a discontinuous mode.

International Publication No. WO2010 / 023978A1

  In the present invention, as control of an insulation type DC-DC converter including a switching element, the output current is suppressed from changing when switching from peak current control to PI control, or output when switching from PI control to peak current control. It is an object of the present invention to provide a technique capable of suppressing fluctuations in current.

  The control method of the present embodiment is a control method for an isolated DC-DC converter including a switching element, and proportional control is performed so that a difference between an output current of the isolated DC-DC converter and a target current becomes zero. By controlling the switching element using the change in the output current from the PI control for controlling the output current to the target current for the next control cycle from the PI control for controlling the output current. When switching to peak current control for controlling the output current in the next control cycle by adjusting the duty ratio of the signal, the duty ratio of the control signal determined by the PI control and the peak current control The difference from the duty ratio of the control signal is added to the duty ratio of the control signal obtained by the peak current control, and after the addition When controlling the switching element or switching from the peak current control to the PI control by a control signal of a duty ratio, the target current of the current control cycle set by the PI control is controlled by the peak current control. The switching element is controlled by using the output current of the previous control cycle and using the target current after the replacement.

  Thereby, when switching from 1st control to 2nd control, the fluctuation | variation of a control result can be suppressed. Therefore, it is possible to suppress fluctuations in the output current when switching from peak current control to PI control or switching from PI control to peak current control as control of an insulated DC-DC converter including a switching element.

  ADVANTAGE OF THE INVENTION According to this invention, when switching from peak current control to PI control as control of an insulation type DC-DC converter provided with a switching element, or when switching from PI control to peak current control, it can suppress that an output current fluctuates. .

It is a figure which shows the insulation type DC-DC converter of this embodiment. It is a flowchart which shows operation | movement of a control circuit. It is a figure which shows an example of the output current at the time of control switching. It is a figure which shows an example of the output current at the time of control switching.

FIG. 1 is a diagram illustrating an isolated DC-DC converter according to the present embodiment.
An insulated DC-DC converter 1 shown in FIG. 1 is, for example, a charger for charging an in-vehicle battery, and supplies an output current corresponding to a target current input from the outside to the in-vehicle battery. The insulated DC-DC converter 1 includes a capacitor 2, switching elements 3 to 6, a transformer 7, a rectifier circuit 8, a smoothing circuit 9, a control circuit 10, voltage detection units 11 and 12, currents, and the like. And a detector 13. The switching elements 3 to 6 are not limited to MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) but may be IGBTs (Insulated Gate Bipolar Transistors) or bipolar transistors.

The rectifier circuit 8 includes diodes 14 to 17. The circuit configuration of the rectifier circuit 8 is not particularly limited.
The smoothing circuit 9 includes an inductor 18 and a capacitor 19.

  The capacitor 2 is provided at the input stage of the isolated DC-DC converter 1. The switching elements 3 and 4 are connected in series to each other and connected to the capacitor 2 in parallel. The switching elements 5 and 6 are connected in series to each other and are connected in parallel to the switching elements 3 and 4. One end of the primary coil of the transformer 7 is connected to the connection point of the switching elements 5 and 6, and the other end of the primary coil of the transformer 7 is connected to the connection point of the switching elements 3 and 4. The capacitor 2 and the switching elements 4 and 6 are connected to the primary side ground of the insulated DC-DC converter 1. The cathode terminal of the diode 14 is connected to one end of the inductor 18 and the cathode terminal of the diode 16, and the anode terminal of the diode 14 is connected to one end of the secondary coil of the transformer 7 and the cathode terminal of the diode 15. The anode terminal of the diode 16 is connected to the other end of the secondary coil of the transformer 7 and the cathode terminal of the diode 17. The anode terminals of the diodes 15 and 17 are each connected to the secondary side ground of the insulated DC-DC converter 1. The capacitor 19 is provided at the output stage of the insulated DC-DC converter 1. The other end of the inductor 18 is connected to one end of the capacitor 19. The other end of the capacitor 19 is connected to the secondary side ground of the insulation type DC-DC converter 1.

  The switching elements 3 and 6 and the switching elements 4 and 5 are alternately turned on and off by the control signals S1 to S4, whereby the input power is converted into AC power and transmitted from the primary coil of the transformer 7 to the secondary coil. The AC power transmitted to the secondary coil is rectified by the rectifier circuit 8, smoothed by the smoothing circuit 9, and output.

  The voltage detection unit 11 detects a voltage (voltage applied to the inductor 18) Vin input to the secondary coil side of the transformer 7, and the voltage detection unit 12 detects the output voltage Vout of the insulation type DC-DC converter 1. The voltage detection units 11 and 12 are, for example, voltmeters.

The current detector 13 detects the output current (current flowing through the inductor 18) IL of the isolated DC-DC converter 1. The current detection unit 13 is an ammeter, for example.
The control circuit 10 performs peak current mode control (PCMC) and PI (P: Proportional, I: Integral) control using the input voltage Vin, the output voltage Vout, and the output current IL. Further, the control circuit 10 controls the output current IL by adjusting the duty ratios of the control signals S1 to S4 by performing peak current control and PI control. For example, the control circuit 10 calculates D1 = 1 / Vin {L × (Itgt−IL) / m × T + 2 × Vout} −D0 at the time of peak current control, thereby controlling the control signals S1 to S4 in the next control cycle. The duty ratio D1 is obtained. Note that L represents the inductance value of the inductor 18, Itgt represents the target current of the next control cycle, m represents the control cycle, T represents the switching cycle, and D0 represents the control signals S1 to S4 in the current control cycle. The duty ratio is shown. For example, the control circuit 10 calculates the duty ratio D1 of the control signals S1 to S4 in the next control cycle by calculating D1 = Kp × ΔIL + Ki × ΣΔIL during PI control. ΔIL represents the difference between the target current Itgt and the output current IL in the current control cycle, Kp represents the coefficient of the proportional control term, and Ki represents the coefficient of the integral control term. For example, the control circuit 10 performs peak current control in the continuous mode in which the target current Itgt is large and the output current IL varies with a value larger than zero, and the period in which the target current Itgt is small and the output current IL is zero PI control is performed in a discontinuous mode that includes and changes. The control circuit 10 is configured, for example, as a CPU (Central Processing Unit), a multi-core CPU, a programmable device (FPGA (Field Programmable Gate Array), a PLD (Programmable Logic Device), or the like, and is stored in a storage unit (not shown). The CPU, a programmable device, or a PLD reads out and executes the stored program, thereby realizing the operation of the control circuit 10.

FIG. 2 is a flowchart showing the operation of the control circuit 10.
First, when an instruction to start charging is input (S11: Yes), the control circuit 10 determines whether to perform PI control (S12). For example, the control circuit 10 determines to perform PI control when the output current IL is equal to or less than the threshold value, and determines to perform peak current control when the output current is greater than the threshold value.

  Next, when the control circuit 10 determines that PI control is to be performed (S12: Yes), an instruction to end charging is input (S14: Yes) or until it is determined to switch to peak current control (S15: Yes), PI control is continued (S13 to S15). For example, when the output current IL is larger than the threshold value, the control circuit 10 determines to switch from PI control to peak current control.

  Next, when the control circuit 10 determines to switch to peak current control (S15: Yes), the duty ratio D0 (current operation amount) of the current control cycle obtained by PI control and the next time obtained by peak current control. The difference from the control cycle duty ratio D1 (next operation amount) is obtained, and the difference is added to the duty ratio D1 of the next control cycle obtained by the peak current control (S16) to perform the peak current control ( S17). In the peak current control, the duty ratio D1 of the control signals S1 to S4 is controlled so that the output current IL follows the target current Itgt with a certain error. Therefore, as shown in FIG. 3 (a), when the target current Itgt gradually increases, if the control is simply switched from the PI control to the peak current control, the output that has followed the target current Itgt by the PI control. The current IL is suddenly lowered by a certain error by the peak current control, and the output current IL is fluctuated. Therefore, in the isolated DC-DC converter 1 of the present embodiment, the difference between the duty ratio D0 of the current control cycle obtained by PI control and the duty ratio D1 of the next control cycle obtained by peak current control is obtained, By adding the difference to the duty ratio D1 of the next control cycle obtained by the peak current control, the duty ratio becomes smaller at the time of control switching, so that the duty ratio is clogged in the subsequent peak current control. As a result, as shown in FIG. 3B, when switching from PI control to peak current control, the output current IL does not drop rapidly, and fluctuations in the output current IL can be suppressed.

  Next, the control circuit 10 continues to perform peak current control until an instruction to end charging is input (S18: Yes) or until it is determined to switch to PI control (S19: Yes) (S16 to S16). S19). First, the difference between the duty ratio D0 and the duty ratio D1 obtained when switching from PI control to peak current control may be used when switching from PI control to peak current control thereafter. Further, when the peak current control is continuously performed, by reducing the difference between the duty ratio D0 and the duty ratio D1 by a constant value, the original output current IL obtained by the target current Itgt (see FIG. 3B). You may make it gradually approach the dotted line).

  If the control circuit 10 determines that the peak current control is to be performed after the input of the charge start instruction (S12) (S12: No), the charge end instruction is input (S21: Yes), or PI Until it is determined to switch to control (S22: Yes), peak current control is continued (S20 to S22). For example, the control circuit 10 determines to switch from peak current control to PI control when the output current IL is equal to or less than a threshold value.

  Next, when the control circuit 10 determines to switch to the PI control (S22: Yes), the control circuit 10 outputs the target current Itgt of the current control cycle set by the PI control in the previous control cycle controlled by the peak current control. In place of the current IL (S23), PI control is performed (S24). As described above, in the peak current control, the duty ratio D1 of the control signals S1 to S4 is controlled so that the output current IL follows the target current Itgt with a certain error. Therefore, as shown in FIG. 4A, when the target current Itgt is gradually reduced, simply switching from the peak current control to the PI control causes the peak current control to follow the target current Itgt with a certain error. Since the output current IL suddenly coincides with the target current Itgt by the PI control, the output current IL rises rapidly and the output current IL fluctuates. Therefore, in the isolated DC-DC converter 1 of the present embodiment, the target current Itgt of the current control cycle set by the PI control is replaced with the output current IL of the previous control cycle controlled by the peak current control. . As a result, as shown in FIG. 4B, when switching from peak current control to PI control, the output current IL does not rise abruptly, and fluctuations in the output current IL can be suppressed.

  Next, the control circuit 10 continues to perform PI control until an instruction to end charging is input (S25: Yes) or until it is determined to switch to peak current control (S26: Yes) (S24 to S26). ).

If the control circuit 10 determines to switch to PI control (S19: Yes), it executes S23 to S26.
If the control circuit 10 determines to switch to peak current control (S26: Yes), it executes S16 to S19.

  As described above, the insulated DC-DC converter 1 according to the present embodiment can suppress fluctuations in the output current IL when switching from PI control to peak current control or switching from peak current control to PI control. That is, when switching from the first control to the second control, fluctuations in the control result can be suppressed.

  Moreover, since the insulation type DC-DC converter 1 of this embodiment can suppress the fluctuation | variation of output current IL, when making it function as a charger of a vehicle-mounted battery, it stabilizes the value of the current sensor provided in the battery side. Can do.

  Moreover, since the insulation type DC-DC converter 1 of this embodiment can suppress the fluctuation | variation of output current IL, the inductor 18 with small inductance value L can be employ | adopted and it can reduce in size.

  In the above embodiment, the peak current control is performed in the continuous mode and the PI control is performed in the discontinuous mode. However, the peak current control is performed in the critical mode where the output current IL varies with zero as the minimum value. You may comprise so that electric current control or PI control may be performed.

DESCRIPTION OF SYMBOLS 1 Insulation type DC-DC converter 2 Capacitors 3-6 Switching element 7 Transformer 8 Rectifier circuit 9 Smoothing circuit 10 Control circuit 11, 12 Voltage detection part 13 Current detection part 14-17 Diode 18 Inductor 19 Capacitor

Claims (2)

In a control method of an isolated DC-DC converter including a switching element,
By performing proportional control and integral control so that the difference between the output current of the insulated DC-DC converter and the target current becomes zero, the output of the current control cycle is changed from the PI control that controls the output current. By adjusting the duty ratio of the control signal of the switching element using the change in the output current from the current to the target current of the next control cycle, peak current control for controlling the output current of the next control cycle is performed. When switching, the difference between the duty ratio of the control signal obtained by the PI control and the duty ratio of the control signal obtained by the peak current control is added to the duty ratio of the control signal obtained by the peak current control. And the switching element is controlled by the duty ratio control signal after the addition,
Or
When switching from the peak current control to the PI control, the target current of the current control cycle set by the PI control is replaced with the output current of the previous control cycle controlled by the peak current control, and the target after the replacement A control method comprising controlling the switching element by using an electric current. A full bridge circuit that includes a plurality of switching elements, and converts the input DC power to AC power by turning on and off the switching elements, and
A transformer for transmitting AC power converted by the full bridge circuit from the primary coil to the secondary coil;
A rectifier circuit for rectifying AC power transmitted to the secondary coil of the transformer;
A smoothing circuit for smoothing the power rectified by the rectifier circuit;
A current detection unit for detecting a current output from the smoothing circuit;
A control circuit that outputs a control signal for controlling on and off of the plurality of switching elements, using a current output from the current detection unit;
With
The control circuit performs proportional control and integral control so that the difference between the output current of the smoothing circuit and the target current becomes zero, thereby performing PI control for controlling the output current from the PI control for the current control cycle. When switching to peak current control for controlling the output current in the next control cycle by adjusting the duty ratio of the control signal using the change in the output current from the output current to the target current in the next control cycle Adding the difference between the duty ratio of the control signal obtained by the PI control and the duty ratio of the control signal obtained by the peak current control to the duty ratio of the control signal obtained by the peak current control;
Or
When switching from the peak current control to the PI control, the target current of the current control cycle set by the PI control is replaced with the output current of the previous control cycle controlled by the peak current control. Isolated DC-DC converter.

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